Currently, it takes 60 votes for the Senate to end debate and move forward on votes. With executive branch nominations, Democrats had threatened to require only a simple majority to end debate, but had said any changes wouldn’t apply to judicial nominations.

Republicans have filibustered two prominent judicial nominations by President Barack Obama. In 2011, Senate Republicans filibustered a final vote on Goodwin Liu, a Berkeley law professor. Mr. Liu, who had been nominated for a federal appeals court opening, subsequently withdrew his name from consideration. This March, Caitlin Halligan, general counsel to the Manhattan district attorney’s office, requested to be withdrawn from consideration for the U.S. Court of Appeals for the D.C. Circuit after Republicans twice filibustered a vote on her nomination.

The next big test could come in the coming months, when Senate Democrats seek confirmation for three nominees for the powerful D.C. Circuit, a court that regularly reviews legal challenges to important federal rules and regulations.

Only one of the nominees, announced in June, has had a hearing before the Senate Judiciary Committee, and confirmation votes are not expected to be scheduled until the fall.

In the weeks leading up to Tuesday’s resolution, Mr. Reid has avoided mention of changing the rules for judicial nominations, focusing on executive branch nominations. In a speech Monday at the Center for American Progress, Mr. Reid said, “On judges, I’m comfortable with our doing what we’re doing. We have to see what happens, but I’m very comfortable with where we are now, and I’m not—not trying to ask for this other places.”

Changing Senate filibuster rules is particularly risky for judicial nominees because unlike executive-branch appointees, federal judges enjoy life tenure once confirmed. In the long history of the judicial-nomination wars, both parties have taken comfort in having the filibuster threat available to oppose judge picks they found particularly objectionable.

But liberal legal groups say Mr. Reid’s willingness to threaten the nuclear option on executive nominees sets a potential precedent for the same to happen with judges.

“If the Republicans continue to obstruct the judicial nominees, I think there will be a second reckoning,” said Caroline Fredrickson, president of the American Constitution Society for Law and Policy, a progressive legal group.

Ms. Fredrickson said she is optimistic that invoking a nuclear option will not be necessary for D.C. Circuit votes to be held. “If this is a moment where cooler heads have prevailed … we can hope for a situation where these highly qualified nominees get through the process,” she said. But she added that legislators have become so frustrated that if Republicans “set up unreasonable blocking” of the nominees, she hopes that Mr. Reid will react accordingly.

The outcome of the fight over executive branch nominations may also give Republicans’ pause.

“It’s possible that [Republicans] will rethink the strategy of blocking the D.C. Circuit nominees, now that they know it may very well end in another one of these embarrassing fights where they end up losing,” said Ian Millihser, senior constitutional policy analyst at the Center for American Progress Action Fund. But if they don’t, Democrats have proven in this week’s discussions that they have the ability to push for what they want, he said.

Nan Aron, president of the Alliance for Justice, a liberal group,commendedthenuclear option as a way to end the “unprecedented number of filibusters” engaged in by Republican legislators. She said she would support the option’s use in the event that Republicans seek to block Mr. Obama’s D.C. Circuit nominations, calling their obstruction a “political effort to prevent the president from carrying out his constitutional task.”

The nuclear option might be effective in the short term, but it would have come at a cost — “the remaining collegiality in the Senate,” said Michael Gerhardt, director of the University of North Carolina Center on Law and Government.

“If the rules change, then you can expect the Senate to change as well,” he said. Relations would significantly worsen among legislators, and the “integrity of the institution” would be damaged, he said.

University of Pittsburgh Professor of Law Arthur Hellman said that there exists a key difference between judicial and executive nominees. While it makes sense for a president to be able to choose officials who will be implementing his program, the issue is more complicated for judicial nominees, since “it is not their job to carry out the president’s agenda.”

Senate watchers have warned that if Democrats push the issue too hard, they will be met with swift retaliation if they lose control of the Senate in 2014 or of the White House in 2016.

Democrats are not unfamiliar with the practice of filibustering judicial nominees — in 2003, Miguel Estrada, nominated by former president George W. Bush, withdrew his name from consideration after Democrats filibustered a vote on his nomination. Democrats mounted filibusters on other Bush judicial picks as well, prompting Senate Republicans to threaten “nuclear” rule changes of their own to outlaw the filibusters.

The showdown was averted when a bipartisan gang of 14 senators struck a deal that allowed some Bush judicial nominations to go through in exchange for taking the nuclear option off the table.

Some conservative legal groups said they are focusing on making sure Senate rules are evenly applied, no matter which party is in power.

“It’s one thing if we have a system where everyone is playing by the same rules,” said Carrie Severino, chief council and policy director for the Judicial Crisis Network. “But to switch the rules while you’re in power and try to do the opposite while you’re in the minority – that doesn’t seem like a fair way to do it.”

About Washington Wire

Washington Wire is one of the oldest standing features in American journalism. Since the Wire launched on Sept. 20, 1940, the Journal has offered readers an informal look at the capital. Now online, the Wire provides a succession of glimpses at what’s happening behind hot stories and warnings of what to watch for in the days ahead. The Wire is led by Reid J. Epstein, with contributions from the rest of the bureau. Washington Wire now also includes Think Tank, our home for outside analysis from policy and political thinkers.